What are the Radioactive Byproducts of Depleted Uranium (Uranium-238)? Here are the Radioactive Byproducts of Depleted Uranium (Uranium-238) [ pour la version française ] The chart given below lists all of the decay products of uranium-238 in their order of appearance. Uranium-238 is also referred to as '' depleted uranium ''. Each radioactive element on the list gives off either alpha radiation or beta radiation -- and sometimes gamma radiation too -- thereby transforming itself into the next element on the list. When uranium ore is extracted from the earth, most of the uranium is removed from the crushed rock during the milling process, but the radioactive decay products are left in the tailings. Thus 85 percent of the radioactivity of the original ore is discarded in the mill tailings . Depleted uranium remains radioactive for literally billions of years, and over these long periods of time it will continue to produce all of its radioactive decay products; thus depleted uranium actually becomes more radioactive as the centuries and millennia go by because these decay products accumulate.

The horizontal bar beside the name of each decay product indicates the " half life " of that particular substance, measured on a logarithmic scale (each half-inch to the right represents multiplication by a factor of one thousand). Lead-206, the last element on the list, is not radioactive. It does not decay, and therefore has no half-life. What is the ''half-life'' of a radioactive element? The half-life of a radioactive element is the time it takes for half of its atoms to decay into something else. For example, the half-life of radium-226 is 1600 years (as indicated on the chart given above). Therefore, in 1600 years, one gram of radium-226 will turn into half a gram of radium-226 and half a gram of something else (the radioactive decay products of radium). After another 1600 years have elapsed, only a quarter of a gram of the original radium-226 will remain. The quantity of any radioactive element will diminish by a factor of a thousand (1 000) during the span of 10 half-lives.

Thus, in 16 000 years, one gram of radium-226 will decay into a milligram of radium-226 and 999 milligrams of other decay products. Similarly, in 760 000 years, one gram of thorium-230 will be reduced to a milligram (because of the 76 000 year half-life of thorium-230, which is indicated on the chart above). Since March 27th 1996, there have been over 100,000 outside visitors to the CCNR web site, plus (counter reset July 2nd 1998 at midnight) Uranium: Its Uses and Hazards - Institute for Energy and Environmental Research Uranium: Its Uses and Hazards Some of the terms used in this factsheet are defined in IEER’s on-line glossary . First discovered in the 18th century, uranium is an element found everywhere on Earth, but mainly in trace quantities. In 1938, German physicists Otto Hahn and Fritz Strassmann showed that uranium could be split into parts to yield energy.

Uranium is the principal fuel for nuclear reactors and the main raw material for nuclear weapons. Natural uranium consists of three isotopes: uranium-238, uranium-235, and uranium-234. Uranium isotopes are radioactive. The nuclei of radioactive elements are unstable, meaning they are transformed into other elements, typically by emitting particles (and sometimes by absorbing particles). This process, known as radioactive decay, generally results in the emission of alpha or beta particles from the nucleus. It is often also accompanied by emission of gamma radiation, which is electromagnetic radiation, like X-rays. These three kinds of radiation have very different properties in some respects but are all ionizing radiation–each is energetic enough to break chemical bonds, thereby possessing the ability to damage or destroy living cells. Summary of Uranium Isotopes 142 245,000 Uranium-238, the most prevalent isotope in uranium ore, has a half-life of about 4.5 billion years; that is, half the atoms in any sample will decay in that amount of time.

Uranium-238 decays by alpha emission into thorium-234, which itself decays by beta emission to protactinium-234, which decays by beta emission to uranium-234, and so on. The various decay products, (sometimes referred to as “progeny” or “daughters”) form a series starting at uranium-238. After several more alpha and beta decays, the series ends with the stable isotope lead-206. URANIUM DECAY CHAIN — Main Branch Read from left to right. Arrows indicate decay. Uranium-238 ==> Lead-206 (stable) Uranium-238 emits alpha particles which are less penetrating than other forms of radiation, and weak gamma rays As long as it remains outside the body, uranium poses little health hazard (mainly from the gamma-rays). If inhaled or ingested, however, its radioactivity poses increased risks of lung cancer and bone cancer. Uranium is also chemically toxic at high concentrations and can cause damage to internal organs, notably the kidneys.

Animal studies suggest that uranium may affect reproduction, the developing fetus, [1] and increase the risk of leukemia and soft tissue cancers. [2] The property of uranium important for nuclear weapons and nuclear power is its ability to fission, or split into two lighter fragments when bombarded with neutrons releasing energy in the process. Of the naturally-occuring uranium isotopes, only uranium-235 can sustain a chain reaction– a reaction in which each fission produces enough neutrons to trigger another, so that the fission process is maintained without any external source of neutrons. [3] In contrast, uranium-238 cannot sustain a chain reaction, but it can be converted to plutonium-239, which can. [4] Plutonium-239, virtually non-existent in nature, was used in the first atomic bomb tested July 16, 1945 and the one dropped on Nagasaki on August 9, 1945. The Mining and Milling Process Traditionally, uranium has been extracted from open-pits and underground mines.

In the past decade, alternative techniques such in-situ leach mining, in which solutions are injected into underground deposits to dissolve uranium, have become more widely used. Most mines in the U.S. have shut down and imports account for about three-fourths of the roughly 16 metric tons of refined uranium used domestically each year — Canada being the largest single supplier. [5] The milling (refining) process extracts uranium oxide (U3O8) from ore to form yellowcake, a yellow or brown powder that contains about 90 percent uranium oxide. [6] Conventional mining techniques generate a substantial quantity of mill tailings waste during the milling phase, because the usable portion is generally less than one percent of the ore. (In-situ leach mining leaves the unusable portion in the ground, it does not generate this form of waste). The total volume of mill tailings generated in the U.S. is over 95 percent of the volume of all radioactive waste from all stages of the nuclear weapons and power production. [7] While the hazard per gram of mill tailings is low relative to most other radioactive wastes, the large volume and lack of regulations until 1980 have resulted in widespread environmental contamination.

Moreover, the half-lives of the principal radioactive components of mill tailings, thorium-230 and radium-226 are long, being about 75,000 years and 1,600 years respectively. The most serious health hazard associated with uranium mining is lung cancer due to inhaling uranium decay products. Uranium mill tailings contain radioactive materials, notably radium-226, and heavy metals (e.g., manganese and molybdenum) which can leach into groundwater. Near tailings piles, water samples have shown levels of some contaminants at hundreds of times the government’s acceptable level for drinking water. [8] Mining and milling operations in the U.S. have disproportionately affected indigenous populations around the globe. For example, nearly one third of all mill tailings from abandoned mill operations are on lands of the Navajo nation alone. [9] Many Native Americans have died of lung cancers linked to their work in uranium mines. Others continue to suffer the effects of land and water contamination due to seepage and spills from tailings piles.

[10] Conversion and Enrichment Uranium is generally used in reactors in the form of uranium dioxide (UO2) or uranium metal; nuclear weapons use the metallic form. Production of uranium dioxide or metal requires chemical processing of yellowcake. Further, most civilian and many military reactors require uranium that has a higher proportion of uranium-235 than present in natural uranium. The process used to increase the amount of uranium-235 relative to uranium-238 is known as uranium enrichment. U.S. civilian power plants typically use 3 to 5 percent uranium-235. Weapons use “highly enriched uranium” (HEU) with over 90 percent uranium-235. Some research reactors and all U.S. naval reactors also use HEU. To enrich uranium, it must first be put in the chemical form uranium hexafluoride (UF6). After enrichment, UF6 is chemically converted to uranium dioxide or metal. A major hazard in both the uranium conversion and uranium enrichment processes comes from the handling of uranium hexafluoride, which is chemically toxic as well as radioactive. Moreover, it reacts readily with moisture, releasing highly toxic hydrofluoric acid.

Conversion and enrichment facilities have had a number of accidents involving uranium hexafluoride. [11] The bulk of waste from the enrichment process is depleted uranium–so-called because most of the uranium-235 has been extracted from it. Depleted uranium has been used by the U.S. military to fabricate armor-piercing conventional weapons and tank armor plating. It was incorporated into these conventional weapons without informing armed forces personnel that depleted uranium is a radioactive material and without procedures for measuring doses to operating personnel. The enrichment process can also be reversed. Highly enriched uranium can be diluted, or “blended down” with depleted, natural, or very low-enriched uranium to produce 3 to 5 percent low-enriched reactor fuel. Uranium metal at various enrichments must be chemically processed so that it can be blended into a homogeneous material at one enrichment level. As a result, the health and environmental risks of blending are similar to those for uranium conversion and enrichment. Regulations in the U.S. In 1983 the federal government set standards for controlling pollution from active and abandoned mill tailings piles resulting from yellowcake production.

The principal goals of federal regulations are to limit the seepage of radionuclides and heavy metals into groundwater and reduce emissions of radon-222 to the air. Mandatory standards for decommissioning nuclear facilities including conversion and enrichment facilities are only now being developed by the U.S. Environmental Protection Agency and the U.S. Nuclear Regulatory Commission (NRC). So far, the NRC has been using guidelines developed by its staff in 1981 to oversee decommissioning efforts. [12] The Future Uranium and associated decay products thorium-230 and radium-226 will remain hazardous for thousands of years. Current U.S. regulations, however, cover a period of 1,000 years for mill tailings and at most 500 years for “low-level” radioactive waste. This means that future generations–far beyond those promised protection by these regulations–will likely face significant risks from uranium mining, milling, and processing activities. Uranium: Known Facts and Hidden Dangers Known Facts and Hidden Dangers invited address by Dr. Gordon Edwards at the World Uranium Hearings Salzburg, Austria Uranium What do we know about uranium?

Well, uranium is the heaviest naturally occurring element on earth. It is a metal, like all other metals, except that it had no commercial value before the mid-twentieth century. Until the last fifty years it was produced only as a byproduct. Thus the entire history of the mining of uranium has taken place during my lifetime. Moreover, a great deal of it has occurred in my homeland, Canada, which was the first country to produce and process uranium as such. The first uranium processed by Canada was used to produce nuclear explosives for the atomic bombs dropped at Hiroshima and Nagasaki in 1945. Indeed, the beginning of the nuclear weapons program marked the beginning of the uranium industry. By 1956, uranium had become the fourth most important export from Canada, after pulp, lumber and wheat; and every ounce of it was used to produce A-bombs and H-bombs for the American -- and, to a lesser extent, the British -- nuclear weapons programs. It was the only use uranium had at that time. Today, Canada remains the world's largest producer and exporter of uranium, ostensibly for peaceful purposes; that is, as fuel for civilian nuclear reactors.

Canada is also one of the very few countries in the world in which uranium mining is currently expanding. In the province of Saskatchewan, there are environmental assessment hearings going on now, this year, having to do with the potential opening of five new uranium mines. This, despite the fact that the price of uranium is lower today than it has ever been. The price has been falling steadily for more than fifteen years, and is now at an all-time low. I hope that those attending this conference will write to the Prime Minister of Canada (c/o House of Commons, Ottawa, Ontario, Canada, K1A 0A6) and to the Premier of Saskatchewan (c/o Saskatchewan Legislature, Regina, Saskatchewan, Canada) asking them not to continue the expansion of this industry. Why? Because uranium is the deadliest metal on earth. As you will see, the scientific evidence fully bears out this conclusion. I would now like to explain why. Both the commercial value and the dangers of uranium are based on two extra-ordinary characteristics which it possesses. First of all, uranium is radioactive. Secondly, uranium is fissionable. These are two quite different properties, however, and they should not be confused.

Radioactivity The phenomenon of radioactivity was accidentally discovered in 1896 when Henri Becquerel put a rock in a drawer. The rock contained uranium, and the drawer contained a photographic plate, which was well-wrapped and shielded from the light. Some weeks later, when Becquerel unwrapped and developed the plate, he found rays of light on the photograph emanating exactly from the point of contact where the rock had been resting on it. Being a scientist, he was astounded. He could think of no possible way in which an inert rock could spontaneously be releasing energy -- especially such a penetrating form of energy. Moreover, the energy release had taken place in total darkness, in the absence of any external stimulation -- there was no chemical reaction, no exposure to sunlight, nor anything else. Becquerel had discovered radioactivity. Marie Curie decided to pursue the mystery further. She got some uranium ore from the Erz mountains, not very far from here.

She chemically separated the uranium from the rest of the crushed rock (she had to crush the rock and dissolve it in acid to get the uranium out, which is what we still do today in mining uranium) and she found that even after the uranium had been removed, the crushed rock remained very radioactive -- much more so than the uranium itself. Here was a mystery indeed. Why is it that eighty-five percent of the radioactivity stays behind in the crushed rock? Starting with many tons of rock, Madame Curie proceeded to separate out all the chemical elements she knew. It was painstaking work. Finally she was left with a small beaker of concentrated, highly radioactive liquid. By evaporating the water, she felt sure she would discover whatever was causing this intense radioactivity. But when the liquid was evaporated, the beaker was, apparently, completely empty. She was deeply disappointed. She couldn't fathom what had gone wrong. But when she returned to the laboratory late at night, she found the beaker glowing brightly in the dark, and she realized that it wasn't empty after all. In this way, Marie Curie discovered two new elements: radium and polonium. We now know these are inevitable byproducts of uranium.

By 1906, all the basic facts of radioactivity were known, except for the central mystery as to "why"; this we do not understand. Indeed, science doesn't really understand why anything is the way it is. All science can do is describe how things behave. Science tells us, for example, that all material things are made up of tiny atoms. The atoms found in most substances are remarkably stable, but in the case of radioactive materials, the atoms are unstable. Consider the water in this glass. It is made up of stable atoms. Pure water is made up of hydrogen and oxygen atoms, and these atoms are, as far as science can determine, eternal and unchangeable. The very same atoms of hydrogen and oxygen that are in this glass of water were around, in some other combinations, in the days of the dinosaurs. But radioactive substances have unstable atoms which can and will explode microscopically, and when they do, they give off a burst of energy. This process is called "radioactive disintegration" or "radioactive decay". When radioactive atoms explode, they give off highly energetic charged particles of two types: alpha and beta. These are particles, they're not invisible rays.

They are like pieces of shrapnel from an explosion. And this microscopic shrapnel does great damage because of the high energy of the particles which are given off. Decay Products When a radioactive atom explodes, that atom is changed permanently into a new substance. And radium turns out to be one of the results of exploding uranium atoms. So wherever you find uranium on the earth, you will always find radium with it because it is one of about a dozen so-called "decay products" of uranium. To be more precise, when uranium disintegrates it turns into a substance called protactinium, which is also radioactive. And when that disintegrates it turns into a substance named thorium, which is likewise radioactive. When thorium disintegrates it turns into radium; when radium disintegrates it turns into radon gas. And when radon gas atoms disintegrate, they turn into what are called the "radon daughters", or "radon progeny", of which there are about half a dozen radioactive materials, including polonium. Finally, in this progression, you end up with a stable substance, which in itself is highly toxic: lead.

But because the radioactivity of the other materials is so much more dangerous than this toxic heavy metal, people don't even talk about the lead at the end of the chain. They think that once all the radioactivity is gone, what's left is perfectly safe. It isn't -- but the lead that remains is just a whole lot less dangerous than the radioactive materials that produced it. So all the radioactive decay products of uranium remain in the crushed rock when uranium is separated from the ore. That's why Marie Curie found most of the radioactivity left behind in the residues, including all the radium and all the polonium. Radium Well, how did the story of uranium progress? Because uranium was less radioactive than its daughter products, it was not valued commercially. But radium was. And radium began to be used principally for two purposes. One was to burn cancerous growths. I should tell you that both Henri Becquerel and Marie Curie suffered grievous burns which were very difficult to heal and which left permanent scars just as a result of handling radium. Other scientists got the idea that if they embedded a needle containing radium inside a cancerous tumor, it would burn the cancer -- and indeed it did.

That was the beginning of cancer therapy using radiation, wherein the harmful effects of atomic radiation are directed against cancerous cells instead of healthy cells. Of course, atomic radiation does similar damage to healthy cells. Now, the other main use for radium was as a luminous paint, because of the glow-in-the-dark phenomenon that Marie Curie had observed. Believe it or not, the price of uranium in the 1920s was $100,000 a gram -- and this is using dollars of the twenties! It was a very expensive commodity, but only very little was needed for any given purpose. Some of it was used to make luminous paint, with which they would paint dials so they could be read even in the dark. Now the young women who painted these things began to get sick. This was first reported by an American dentist called Blum, who said that he had some very young women -- 19 years old, 18 years old, 20 years old -- coming into his dentistry office. Their teeth were falling out, their gums were badly infected and bleeding profusely, they were anemic, their bones were soft, and in some cases their jawbones had spontaneously fractured.

Some of them died of severe anemia. The only thing these women had in common was that they worked in a radium dial painting factory in New Jersey. Blum called this phenomenon "radium jaw". A few years later, the women who had recovered from these symptoms started developing problems in the rest of their skeleton. They suffered weakening of the bone, spontaneous fractures of the hip and of other bones, and growths -- tumors, some of which were cancerous -- in the bones themselves. Now, bone cancer is such an exceedingly rare disease, that there was little doubt that this cancer was caused by exposure to radium. It was discovered that simply by wetting the tip of the brush in order to get a nice clean figure on the dials, these women were ingesting minute quantities of radium. And that was sufficient to cause all these symptoms. When autopsies were performed on the corpses of these women, doctors discovered that in their entire skeleton there were only a few micrograms of radium. This quantity was so small, that no conventional chemical analysis could detect it.

Nevertheless, this tiny amount of radium had distributed itself so thoroughly through their skeleton, that you could take a picture of any one of their bones just by laying it on a photographic plate in a dark room, It is called an auto-radiograph -- that is, an x-ray picture with no x-ray machine. So this was our first introduction to the harmful effects of even minute quantities of such substances. By the way, many of the women who survived this phase of the assault later on developed cancers of the head -- cancer of the sinuses, cancer of the soft palate, and other types of head cancers. We now know how these were caused. Remember, radium is radioactive -- even inside the body. As I told you earlier, when radium atoms disintegrate, they turn into radon gas. So radon gas was being produced inside the bodies of these women. In fact, one test for radium contamination is to check a person's exhaled breath and see if it has radon gas in it; if it does, that person must have radium in his or her body.

In the case of the radium dial painters, the radon gas was being produced in the bones, dissolved in the blood, and pumped by the heart up to the head where it collected in the sinus and other cavities. And there it was irradiating the delicate living tissues and causing head cancers. Radon Now, it so happens that for hundreds of years, going back to the 15th century, there had been reports that miners working in the Erz mountains had been dying at a tremendous rate from some unknown lung diseases. We're talking here about 75 percent mortality in some cases. It wasn't until the late 19th century that the principal disease was diagnosed and found to be lung cancer. At that time, lung cancer was virtually unknown among the surrounding population; yet these miners were experiencing in some cases up to 50 percent lung cancer mortality. The other lung ailments were not lung cancer, but other types of debilitating lung damage. By the 1930s it had been established that this epidemic of lung cancer and other lung diseases was caused by breathing radioactive materials in the atmosphere of the mine. In animal experiments, radon gas was identified as the main killer.

Uranium finally acquired commercial value in 1942, when we discovered that we could make atomic bombs with it. Only then did we start mining uranium for itself and not as a byproduct of something else. A few years earlier, in 1938, it was discovered that uranium is not only radioactive, it is also fissionable, which makes it unique among all naturally occurring radioactive materials. When uranium atoms undergo the fission process, large amounts of energy are released. Unlike the process of radioactive decay, which cannot be turned on and off, nuclear fission can be controlled. The energy release caused by fission can be speeded up, slowed down, started or stopped. It can be used to destroy cities in the form of nuclear weapons, or to boil water inside a nuclear reactor. Suddenly, uranium was in demand. We sent miners into the mines in North America at a permissible level of radiation exposure which was comparable to the levels that those miners in the Erz mountains had been getting back in the 19th century. And of course, the results were entirely predictable: an epidemic of lung cancer and other lung diseases. One has to ask therefore: Why were these consequences not predicted and prevented?

Radon Daughters The answer is, in part, that the scientists refused to believe that such a small amount of radon gas could cause such a huge increase in cancer. As it turns out, the scientists were wrong. One of the basic things they overlooked, is that if you take a sample of radon gas -- right now, if I filled a tube with radon gas in front of your eyes, and measured the radiation in that tube -- within three hours, the level of radioactivity would increase by a factor of about five. Why? As the radon atoms disintegrate, they produce other radioactive substances. And so, in fact, you have a multiplication of new radioactive materials which weren't there to begin with. This is one of the things the scientists overlooked. So that when the miners go into a mine where the radon has been collecting for several hours, it's five times as radioactive as radon in the laboratory. And those other substances -- the radon daughters -- are extremely dangerous. The worst of the radon daughters, by the way, is a substance called polonium -- the same polonium that Marie Curie discovered so many years ago.

Recent scientific evidence shows that polonium is, in many circumstances, at least as toxic as plutonium, and in some cases more toxic. Nuclear Fission Now, what is that property that made uranium commercially valuable? It's called fissionability. More precisely, uranium is called a "fissile" material. Let me explain what that means. Yes, uranium atoms are radioactive, and so they will disintegrate if you just leave them alone; but what happens if you poke them? What happens if you bombard uranium atoms with tiny particles called neutrons? It turns out that in that case, you can force a much more violent disintegration of the atom, which is called fission. When fission occurs, the uranium atom doesn't just disintegrate, it actually breaks apart into two or three large chunks. In the process it gives off some extra neutrons, and it also gives off about 400 times as much energy as is produced by a radioactive disintegration event. Now, the fact that fission is triggered by a neutron makes it quite different from normal radioactivity. Radioactivity is not triggered, and therefore science does not know how to control it.

We have no mechanism for speeding up, slowing down, starting or stopping radioactivity. That's why radioactive wastes are such a problem. But with fission, we can start it, stop it, and control it, just by maintaining control over the extra neutrons that are produced at each stage. Starting with just one neutron, we can split one uranium atom, and the extra neutrons can go on to split two more uranium atoms, giving even more neutrons which can then split four atoms, which can then split eight atoms, and so on. In this way, forty quintillion uranium atoms can be split with only sixty generations of splittings, all triggered by a single neutron. [A quintillion is a billion billion, or a million million million.] This whole "chain reaction", as it is called, takes place in less than a thousandth of a second. That is really what constitutes the atomic bomb. Fission Products You may now realize that all of the radioactive materials which escape from an atomic bomb when it explodes, are basically the broken bits of uranium atoms. These are new radioactive materials, called "fission products", which are created by the splitting of uranium atoms. There are hundreds of them.

They all have different names, and different chemical and biologically properties. Most of them did not exist in nature before the advent of nuclear technology. You see, uranium travels in many disguises. In every sample of uranium ore, one finds radium -- but radium is, in a certain sense, just a transformation of uranium. Speaking loosely, one could say that it is a disguised form of uranium. It is just one of the many elements in the chain of decay. Similarly with polonium. Similarly with radon gas. These are all just different manifestations of uranium, so to speak, resulting from radioactive decay. And similarly with the fallout from atomic bombs; all those radioactive materials which are released by nuclear explosions -- such as iodine-131, strontium-90, cesium-137, krypton-85, and all the rest -- they are all broken bits of uranium atoms. They are additional disguises for uranium, resulting from nuclear fission. The radioactive poisons that were released from the Chernobyl reactor are also broken bits of uranium atoms.

Incidentally, 80 percent of the total radiation dose delivered by the Chernobyl accident worldwide was caused by the escape of just a couple of kilograms of radioactive materials from the damaged nuclear plant. It doesn't take much.... To this day, the sheep in Wales are unsuitable for human consumption because of contamination by one particular by-product of the Chernobyl accident called cesium-137. But every atom of cesium-137 from Chernobyl started out as an atom of uranium. These radioactive materials, which are called fission products -- the ones in the bomb fallout and which in nuclear reactors -- should not be confused with the other radioactive materials I told you about earlier, which are the decay products of uranium. The decay products of uranium are due to radioactive disintegration. They are about two dozen in number, and they occur in nature because uranium does. When you talk about fission products, however, you are dealing with completely different substances. They are created only inside nuclear weapons or nuclear reactors. They are the leftover pieces of uranium atoms which have been violently broken apart by the fission process.

There are over 300 of them altogether, when you consider that -- being radioactive -- each of the fission products also has its own decay products! Health Effects of Radioactive Materials And so this one material, uranium, is responsible for introducing into the human environment a tremendously large range of radioactive materials which are all very inimical to biological organisms. These are not invisible rays, they are materials. They get into our water, our food, and the air we breathe. They're exactly like other materials except for the fact that they're radioactive. Take, for instance, radioactive iodine. It behaves just like ordinary iodine, which is not radioactive. Why is there iodine in our table salt? Well, it's one of the few examples of preventative medicine we have. The iodine, when it's eaten in the table salt, goes to the thyroid gland, and there it helps to prevent a disease of the thyroid gland called "goiter". Radioactive iodine does exactly the same thing. If a child or an adult gets radioactive iodine in the diet, the radioactive iodine goes to the thyroid too, and it also helps to prevent goiter.

But while it's there, the atoms explode, and the shrapnel rips through the cells of the body, and in the process breaks thousands of chemical bonds randomly. It's like throwing a grenade into a computer. The probability of getting an improvement in a computer by throwing a grenade into it is very small, and similarly with radiation events and human cells. Now, the cells that die are really no problem, as long as not too many of them die. They can be replaced. The ones that are particularly dangerous are the ones that survive. Those damaged cells can develop into cancers. You can also have damage to germ cells -- eggs and sperm -- leading to genetically damaged children, grandchildren, or great-grandchildren. As Alice Stewart mentioned in her talk, there are two categories of human illness that everyone agrees can be caused by exposure to atomic radiation even at very low levels. They are (1) cancers of all kinds, and also (2) genetic mutations -- which can be caused right down to the lowest levels of radiation exposure.

Most scientists believe that these harmful effects are linearly related to the dose, so that if the dose is doubled, the number of cancers and genetic defects will also be doubled, and if the dose is cut in half, only half as many cancers and genetic defects will be seen. It is important to realize that if a damaging dose is spread out among a very large population, so that each individual receives only a very small portion of the total dose, the number of cancers and genetic defects is in no way diminished. Thus, in the case of radioactive pollution, dilution is no solution at all. However, there is one other effect of radiation at low levels which wasn't mentioned in the previous talk, and I would like to just mention it here. It has now been confirmed by the scientific community -- only in recent years, by the way -- that mental retardation is caused by radiation exposure in the womb. This type of biological damage also seems to be linear, that is, proportional to dose, right down to the lowest levels of exposure. There doesn't seem to be any cut-off point.

And so we have now discovered yet a third category of documented and scientifically accepted harmful effects of radiation and that is mental retardation in children who were irradiated while still in the womb. Uranium Tailings Now, if I could just wrap up, I have to tell you something extremely important. The title of my talk was "Known facts and hidden dangers". I've told you a bit about the known facts. Now for at least one of the hidden dangers. When we extract uranium from the ground, we dig up the rock, we crush it and we leave behind this finely pulverized material -- it's like flour. In Canada we have 200 million tons of this radioactive waste, called uranium tailings. As Marie Curie observed, 85 percent of the radioactivity in the ore remains behind in that crushed rock. How long will it be there? Well, it turns out that the effective half-life of this radioactivity is 80,000 years. That means in 80,000 years there will be half as much radioactivity in these tailings as there is today. You know, that dwarfs the entire prehistory of the Salzburg region which goes way back to ancient, ancient times.

Even archaeological remains date back no further than 80,000 years. We don't have any records of human existence going back that far. That's the half-life of this material. And as these tailings are left on the surface of the earth, they are blown by the wind, they are washed by the rain into the water systems, and they inevitably spread. Once the mining companies close down, who is going to look after this material forever? How does anyone, in fact, guard 200 million tons of radioactive sand safely forever, and keep it out of the environment? In addition, as the tailings are sitting there on the surface, they are continually generating radon gas. Radon is about eight times heavier than air, so it stays close to the ground. It'll travel 1,000 miles in just a few days in a light breeze. And as it drifts along, it deposits on the vegetation below the radon daughters, which are the radioactive byproducts that I told you about, including polonium. So that you actually get radon daughters in animals, fish and plants thousands of miles away from where the uranium mining is done.

It's a mechanism for pumping radioactivity into the environment for millennia to come, and this is one of the hidden dangers. Conclusion All uranium ends up as either nuclear weapons or highly radioactive waste from nuclear reactors. That's the destiny of all the uranium that's mined. And in the process of mining the uranium we liberate these naturally occurring radioactive substances, which are among the most harmful materials known to science. Couple this with the thought that nuclear technology never was a solution to any human problem. Nuclear weapons do not bring about a sane world, and nuclear power is not a viable answer to our energy problems. We don't even need it for electricity. All you need for conventional electricity generation is to spin a wheel, and there's many ways of doing it: water power, wind power, geothermal power, etc. In addition, there are other methods for producing electricity directly: solar photovoltaics, fuel cells, and so on. What we have here, in the case of nuclear power, from the very beginning, is a technology in search of an application. So, I think that we as a human community have to come to grips with this problem and say to ourselves and to others that enough is enough.

We do not want to permanently increase our radiation levels on this planet. We have enough problems already. Thank you. uranium: Isotopes and Radioactive Decay uranium Isotopes and Radioactive Decay Naturally occurring uranium is a mixture of three isotopes. The most abundant (greater than 99%) and most stable is uranium-238 ( half-life 4.5×109 years); also present are uranium-235 (half-life 7×108 years) and uranium-234 (half-life 2.5×105 years). There are 16 other known isotopes. Uranium-238 is the parent substance of the 18-member radioactive decay series known as the uranium series (see radioactivity ). Some relatively long-lived members of this series include uranium-234, thorium-230, and radium-226; the final stable member of the series is lead-206.

Uranium-235, also called actinouranium, is the parent substance of the so-called actinium series, a 15-member radioactive decay series ending in stable lead-207; protactinium-231 and actinium-227 are the relatively stable members of this series. Because the rate of decay in these series is constant, it is possible to estimate the age of uranium samples (e.g., minerals) from the relative amounts of parent substance and final product (see dating ). Sections in this article: Radioactive decay and radioactivity Radioactive decay and radioactivity 8-11-99 The nucleus When we looked at the atom from the point of view of quantum mechanics, we treated the nucleus as a positive point charge and focused on what the electrons were doing. In many cases, such as in chemical reactions, that's all that matters; in other cases, such as radioactivity, or for nuclear reactions, what happens in the nucleus is critical, and the electrons can be ignored. A nucleus consists of a bunch of protons and neutrons; these are known as nucleons.

Each nucleus can be characterized by two numbers: A, the atomic mass number, which is the total number of nucleons; and Z, the atomic number, representing the number of protons. Any nucleus can be written in a form like this: where Al is the element (aluminum in this case), the 27 is the atomic mass number (the number of neutrons plus the number of protons), and the 13 is Z, the atomic number, the number of protons. How big is a nucleus? We know that atoms are a few angstroms, but most of the atom is empty space. The nucleus is much smaller than the atom, and is typically a few femtometers. The nucleus can be thought of as a bunch of balls (the protons and neutrons) packed into a sphere, with the radius of the sphere being approximately: The strong nuclear force What holds the nucleus together? The nucleus is tiny, so the protons are all very close together. The gravitational force attracting them to each other is much smaller than the electric force repelling them, so there must be another force keeping them together. This other force is known as the strong nuclear force; it works only at small distances.

The strong nuclear force is a very strong attractive force for protons and neutrons separated by a few femtometers, but is basically negligible for larger distances. The tug-of-war between the attractive force of the strong nuclear force and the repulsive electrostatic force between protons has interesting implications for the stability of a nucleus. Atoms with very low atomic numbers have about the same number of neutrons and protons; as Z gets larger, however, stable nuclei will have more neutrons than protons. Eventually, a point is reached beyond which there are no stable nuclei: the bismuth nucleus with 83 protons and 126 neutrons is the largest stable nucleus. Nuclei with more than 83 protons are all unstable, and will eventually break up into smaller pieces; this is known as radioactivity. Nuclear binding energy and the mass defect A neutron has a slightly larger mass than the proton. These are often given in terms of an atomic mass unit, where one atomic mass unit (u) is defined as 1/12th of the mass of a carbon-12 atom. Something should probably strike you as being a bit odd here.

The carbon-12 atom has a mass of 12.000 u, and yet it contains 12 objects (6 protons and 6 neutrons) that each have a mass greater than 1.000 u. The fact is that these six protons and six neutrons have a larger mass when they're separated than when they're bound together into a carbon-12 nucleus. This is true for all nuclei, that the mass of the nucleus is a little less than the mass of the individual neutrons and protons. This missing mass is known as the mass defect, and is essentially the equivalent mass of the binding energy. Einstein's famous equation relates energy and mass: If you convert some mass to energy, Einstein's equation tells you how much energy you get. In any nucleus there is some binding energy, the energy you would need to put in to split the nucleus into individual protons and neutrons.

To find the binding energy, then, all you need to do is to add up the mass of the individual protons and neutrons and subtract the mass of the nucleus: The binding energy is then: In a typical nucleus the binding energy is measured in MeV, considerably larger than the few eV associated with the binding energy of electrons in the atom. Nuclear reactions involve changes in the nuclear binding energy, which is why nuclear reactions give you much more energy than chemical reactions; those involve changes in electron binding energies. Radioactive decay Many nuclei are radioactive. This means they are unstable, and will eventually decay by emitting a particle, transforming the nucleus into another nucleus, or into a lower energy state. A chain of decays takes place until a stable nucleus is reached. During radioactive decay, principles of conservation apply. Some of these we've looked at already, but the last is a new one: conservation of energy conservation of momentum (linear and angular) conservation of charge conservation of nucleon number Conservation of nucleon number means that the total number of nucleons (neutrons + protons) must be the same before and after a decay. There are three common types of radioactive decay, alpha, beta, and gamma.

The difference between them is the particle emitted by the nucleus during the decay process. Alpha decay In alpha decay, the nucleus emits an alpha particle; an alpha particle is essentially a helium nucleus, so it's a group of two protons and two neutrons. A helium nucleus is very stable. An example of an alpha decay involves uranium-238: The process of transforming one element to another is known as transmutation. Alpha particles do not travel far in air before being absorbed; this makes them very safe for use in smoke detectors, a common household item. Beta decay A beta particle is often an electron, but can also be a positron, a positively-charged particle that is the anti-matter equivalent of the electron. If an electron is involved, the number of neutrons in the nucleus decreases by one and the number of protons increases by one. An example of such a process is: In terms of safety, beta particles are much more penetrating than alpha particles, but much less than gamma particles. Gamma decay The third class of radioactive decay is gamma decay, in which the nucleus changes from a higher-level energy state to a lower level. Similar to the energy levels for electrons in the atom, the nucleus has energy levels.

The concepts of shells, and more stable nuclei having filled shells, apply to the nucleus as well. When an electron changes levels, the energy involved is usually a few eV, so a visible or ultraviolet photon is emitted. In the nucleus, energy differences between levels are much larger, typically a few hundred keV, so the photon emitted is a gamma ray. Gamma rays are very penetrating; they can be most efficiently absorbed by a relatively thick layer of high-density material such as lead. A list of known nuclei and their properties can be found in the chart of the nuclides at the Brookhaven National Laboratory. Radioactivity Making a precise prediction of when an individual nucleus will decay is not possible; however, radioactive decay is governed by statistics, so it is very easy to predict the decay pattern of a large number of radioactive nuclei. The rate at which nuclei decay is proportional to N, the number of nuclei there are: Whenever the rate at which something occurs is proportional to the number of objects, the number of objects will follow an exponential decay.

In other words, the equation telling you how many objects there are at a particular time looks like this: The decay constant is closely related to the half-life, which is the time it takes for half of the material to decay. Using the radioactive decay equation, it's easy to show that the half-life and the decay constant are related by: The activity of a sample of radioactive material (i.e., a bunch of unstable nuclei) is measured in disintegrations per second, the SI unit for this being the becquerel. Understanding half-life using M&M's Please note that M&M's are perfectly safe, and are not radioactive. M&M's can be used as a model of a sample of radioactive nuclei, however, because when they lie on a flat surface they can be in one of just two states - they can lie with the M up or with the M down. Let one of those states (M down, say) represent decayed nuclei. With a package of M&M's, you can model a sample of decaying nuclei like this: step 1 - count the number of M&M's you have. step 2 - throw them onto a flat surface, and count the number of M&M's with M up.

Remove all the M down M&M's from the sample. step 3 - repeat step 2 until you have no M&M's left. Every time you throw the M&M's, you've gone through one more half-life. Here's the data from one trial: The above is just a single trial; you should try it yourself to see what you get. This trial shows something interesting, however. When you have a large number of particles, they follow the predicted behavior very closely. When you only have a small number, the inherent randomness of the decay process is a little more obvious. Radioactive dating Radioactivity is often used in determining how old something is; this is known as radioactive dating. When carbon-14 is used, as is often the case, the process is called radiocarbon dating, but radioactive dating can involve other radioactive nuclei. The trick is to use an appropriate half-life; for best results, the half-life should be on the order of, or somewhat smaller than, the age of the object.

Carbon-14 is used because all living things take up carbon from the atmosphere, so the proportion of carbon-14 in the carbon in a living organism is the same as the proportion in the carbon-14 in the carbon in the atmosphere. For many thousands of years this proportion has been about 1 atom of C-14 for every 8.3 x 1011 atoms of carbon. When an organism dies the carbon-14 slowly decays, so the proportion of C-14 is reduced over time. Carbon-14 has a half life of 5730 years, making it very useful for measuring ages of objects that are a few thousand to several tens of thousands of years old. To measure the age of something, then, you measure the activity of carbon-14, and compare it to the activity you'd expect it to have if it was brand new. Plugging these numbers into the decay equation along with the half-life, you can calculate the time period over which the nuclei decayed, which is the age of the object.

Question: Which element is the final result of the radioactive decay of uranium?
Answer: LEAD